The long term objective of this proposal is to understand the molecular mechanisms that determine axon adhesion. and guidance during neurodevelopment. This fundamental understanding will aid in the prevention of neurological birth defects and in the induction of nerve regeneration after injury or degenerative disease. Knowledge of the molecules required for the formation of correct neurocircuitry may lead to treatment of neurological and psychiatric disorders. The proposal focuses on adhesion molecules in grasshopper neurodevelopment. It has been suggested that these molecules dictate axon guidance by establishing labeled pathways that growth cones recognize and adhere to. A new technique called chromophore assisted laser inactivation (CALI) will be used to inactivate these adhesion molecules during the development of identified neurons in the grasshopper limb bud and CNS with an unprecedented spatial and temporal resolution. CALI uses chromophore-labeled antibodies to target laser energy to proteins of interest, thereby denaturing them, without otherwise affecting the embryo. Fasciclin I has been shown to play a role in axon adhesion in the limb bud pioneer neurons. This study will investigate when and where fasciclin I is required for correct axon guidance. The interaction of fasciclin I with Abelson tyrosine kinase will be investigated to test the hypothesis that adhesion molecules signal intracellular changes that direct axon guidance. Fasciclin II, neuroglian, Notch protein and PS2 antigen will also be inactivated at discrete times in specific cellular locations to determine their respective roles in axon guidance. This study is a molecular dissection of axon guidance using a unique approach that generates spatially and temporally specific lesions of protein function in the grasshopper embryo; this would not be otherwise possible. In addition to providing insight into the molecular specification of axon guidance, this project will develop techniques that will have significant utility in addressing many diverse questions in the biomedical sciences.